Environmental qualification of insulation systems for nuclear applications

For a recent contract, the user specified that the primary heat transport pump and the shutdown pump motors be environmentally qualified (EQ) for the applications. This meant that the complete motors, including the insulation, systems would be tested along the requirements set forth in IEEE 323, IEEE 334, and IEEE 344. The physical sizes of the machines prevented the actual units from being tested, and hence, component testing became necessary. To environmentally qualify a stator insulation system, including a loss of coolant accident (LOCA) toward the end of a 30 year insulation life, requires the manufacture and testing of statorettes. This paper discusses: (1) the types of problems which can be encountered in this type of exercise; (2) the testing and test results for both a 4 kV and a 13.2 kV insulation system; and (3) the results from testing to failure of the coils after the completion of the environmental qualification tests. Results of surge, hi-pot, polarization index, and partial discharge tests are presented.